Flat panel screen displays are designed to display information and images on a screen. They have been extensively used in conjunction with computer systems as computer display screens. Instead of using the large and heavy cathode ray tube technology, many flat panel displays utilize Liquid Crystal Display (LCD) technology. The flat panel LCDs are relatively light weight and have low power consumption. Therefore, the flat panel LCD screen is ideal for use with portable computers where light weight and low power consumption are desired.
However, conventional flat panel LCDs have several problems steming form their structural design. For instance, images formed on the screen within a prior art LCD must be viewed straight on by the computer user by facing the screen directly, otherwise known as a 90 degree view angle. When viewing the flat panel screen tilted or from a vertical or horizontal angle, called "off-axis" viewing, prior art LCD screens may create display distortions because of the optical nature of the display technology. Most often this off-axis viewing leads to contrast degradation and color aberrations.
The display distortions inherent in the prior art LCD are called parallax and are a consequence of off-axis viewing. Parallax is defined as the difference between the observable position of an image on the LCD and the surface of the LCD screen resulting when the angle of view is such that the apparent image is not visibly oriented directly under the corresponding point on the surface of the display. Parallax increases with an increase in the off-axis viewing angle.
FIG. 1 illustrates the parallax problem in a prior art embodiment. The illustration shows a target pixel 112 in an LCD layer 105 and the corresponding target point 114 on the surface of the touch screen or top glass 103. The view location 101 is at an angle to the normal of the display, and so the intersection of the line of sight 102, between the observer location and the target pixel, and the top glass is a point some distance from the target point. The distance between the line of sight/top glass intersection 110 and the target point 114 is the parallax 120 associated with the particular display and particular viewing angle. The parallax is zero for an observer viewing the target pixel head-on such that the line of sight is normal, or perpendicular, to the display surface.
Parallax is a particularly acute problem with touch sensitive screens where the user of the system provides inputs to the system by pointing to, or touching, objects displayed on the screen because the construction of flat panel LCDs causes the image to appear at a position that is not the true tangible screen surface position. The difference in depth between the image position and the surface of the flat panel display is called the image depth. Large image depth contributes to the problem of parallax because the larger the image depth the worse the parallax. In a typical prior art design, the image depth is enlarged when touch sensitive flat panel touch screens are employed because a special thick touch sensitive layer rests on top of the outer layer of the LCD. This touch sensitive layer presents a layer between the displayed image and the viewer through which the viewer must view the display.
As a result of the image depth created by the touch sensitive layer, when the flat panel touch sensitive screen is viewed off-axis the optical position of the image is different from the tangible position on the screen surface. Thus, the apparent position of the pixel is not the same as the position on the surface of the screen vertically correspondent with the electrode grid below responsible for creating the apparent image. This is true because the screen tilt and image depth causes the image to appear in a screen location which is not directly above the image and thus difficult to touch when using thick touch sensitive screens, and is therefore difficult to target when the display is used in a touch sensitive configuration. This is a problem because when such a display is used as a touch screen, the user touches the surface of the display with the expectation that the surface coordinates correlate to the coordinates of the pixels visible within the display. Therefore, if a touch sensitive screen is used with this type of LCD then it is difficult, if not impossible, to accurately select various on-screen items because of the parallax problem.
One answer to this problem is to make the layers through which the image must pass sufficiently thin to reduce the image depth and the parallax.
However, structural support is required to protect the fragile LCD layer because mechanical pressure on an LCD layer can modify the alignment of the molecules of the structure comprising the LCD and can even permanently damage the LCD structure. Furthermore, the thinner the film the more easily it is scratched. Moreover, very thin films frequently peel or separate from the surface of the LCD. Therefore, a sufficient thickness is required for the touch sensitive layer.
Computer systems are often used in video conferencing applications. In the typical prior art video conferencing setup using a computer system, conference participants view a personal computer screen which is displaying the participants at the other end of the conference connection. The images of the conference participants on each end of the connection are captured by a prior art camera mounted on top of or on the side of the video display. As the participants are watching each other on the display and the camera is viewing them from an off-axis angle, eye-to-eye contact is difficult. Consequently there is a requirement for a LCD display having an input function integrated with the pixel display cells where the input function senses image inputs and pen and human touch inputs, and where the input function does not require a separate substrate from that of the LCD.